Paper handling systems frequently include bar code recognition systems. These systems are often employed in mail processing equipment, such as sorters or inserters.
Posts and private carriers frequently provide discounts to mailers who presort mail. The discounts vary from country to country and are often dependent on the level of presort. In general, the more specifically the mail has been sorted in relation to delivery by the post or carrier, the greater the discount. In the United States, mail sorting equipment reduces the cost of sorting mail, which may be from $45 per thousand pieces when manually sorted, to $3 per thousand pieces when automatically sorted. Furthermore, when mailers presort mail before presentation to the United States Postal Service (USPS), the postal discounts from the full postal charge for first class mail presently provided to the mailer by USPS can be as high as 9.5 cents per mail piece.
These mail sortations implemented by the mailer, by the posts or the private carriers, often utilize a multiple pass radix sort algorithm. The United States National Institute of Standards and Technology defines a radix sort as a multiple pass distribution sort algorithm that distributes each item to a bucket according to part of the item's key, beginning with the least significant part of the key. After each pass, items are collected from the buckets, keeping the items in order, then redistributed according to the next most significant part of the key. In a mailing system radix-type sortation, the key can be the delivery point sequence number which may be accessed with reference to a ZIP code, and the bucket can be the destination sortation bin. Use of a radix sort allows mail pieces to be sorted into delivery point sequence (carrier walk sequence) and eliminates the need for the delivery person to sort the mail before delivery. However, in implementing multiple sortations of this type, to achieve a delivery point sequence requires that the ordering or layering of mail from prior sortations be maintained when mail pieces from each of the sortation bins are combined for the next sortation pass.
In processing mail, the systems may read the bar codes applied to the face of the envelope to determine the destination sortation bin for the mail piece during a particular sortation pass. In the United States, USPS POSTal Numeric Encoding Technique (POSTNET) bar codes are printed on the face of the envelope and are read by the bar code reading system. The POSTNET specifications are documented in the USPS Domestic Mail Manual issue 58 in section C840 (bar coding standards for letters and flats) and in USPS Publication 25 (Designing letter mail) in chapter 4. The POSTNET bar code encodes the destination ZIP code (postal code) on the face of the mail piece and is employed for the sortation process. A problem occurs when the imprinted postal code cannot be properly read such as from a POSTNET or other bar code by the sortation equipment. In such a case, the mail piece is outsorted from the sortation run to a reject bin for manual processing. This is a very expensive cost in processing mail. It is particularly problematic because of the requirement for maintaining the careful layering of the mail in for multipass sequence sorts.
This required layering for multipass sequencing is not maintained with respect to the outsorted mail piece. Accordingly, the outsorted mail piece loses its place in the sortation process and must be manually placed in the appropriate sequence if multipass sortation sequencing is to be maintained. The problem may be further compounded since typically a very small time window exists before the next batch of mail is processed for a different delivery area. These problems reduce the mailing handling system productivity and throughput.
Prior attempts to deal with the problem of the bar code reader being unable to accurately read the imprinted code on the mail piece have provided plural bar code readers from different vendors. Since it is known that rejected or unread mail is often properly read when submitted to different readers, in the hope that if one of the bar code readers cannot completely recover a bar code imprinted on a media item, the other bar code reader type would be able to make the full read. The subsequent bar code reader provides another opportunity for a correct read of the imprinted bar code on the mail piece. If any of these bar code readers provide a complete and proper reading of the bar code, the mail piece is not outsorted to a reject bin and is included in the sortation process.
Prior art systems also rerun unread pieces in the system, while the pieces often read on the second attempt by the same reader, these pieces may have lost their sequence position within the multipass sort and therefore may not gain the full benefit of the sortation process. Each pass is a stand alone event, either the bar code read reads the bar code or it does not.
Additionally, the error recovery capability within the USPS POSTNET bar code as explained in the above-noted USPS publications, has been employed to obtain a valid ZIP code from a partially read code. POSTNET encodes each ZIP digit in a cluster of 5 bars (two of which are long and three of which are short). If this requirement is not met, then the digit cluster is known to be corrupted. The modulo 10 check digit (last digit) may then be used to recover a single missing ZIP code digit. It has sometimes been possible to recover two digits in some limited instances. Such recovery has been within a single read of a single POSTNET bar code where two different clusters of five bars (each cluster encoding a numerical digit) are corrupted if there is only one unique possible solution compatible with the known data. Recovery has been by means of a use of a lookup table of possible cluster combinations that provide the solution and are consistent with the check sum data.
Inexpensive tracing and tracking of mail is a feature requested by many postal customers. The USPS developed the PostaL Alpha Numeric Encoding Technique (PLANET) bar code to enable tracing and tracking of mail pieces by providing a unique identifier for each mailing. In combination with the POSTNET bar code identifying the destination, PLANET bar codes make it possible to uniquely identify each mail piece. The encoding scheme is the complement of the POSTNET encoding scheme (three tall bars and two short bars in each cluster of five). Thus, the same bar code reader can operate to read both POSTNET and PLANET bar codes. At the same time, the different symbology conventions make it possible to distinguish the two bar codes (mostly tall vs. mostly short bars). Error correction principles associated with POSTNET codes also apply to PLANET codes. With the use of both the POSTNET and PLANET bar codes, the mail piece is uniquely defined only by the combination of the two bar codes, either code alone is typically insufficient. However, if each of plural bar codes, for example, a POSTNET and a PLANET code, are read with a certain probability, the probability of all bar codes being read is the product of the individual probabilities. The need to read both codes reduces the probability of a full correct reading of the entire bar coding on a mail piece. Thus a 95% read probability of a single bar code will become a 90% probability (0.95*0.95) of reading two bar codes or an 86% probability of reading three.